This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-110675, filed on Apr. 9, 2001; the entire contents of which are incorporated herein by reference.
This invention relates to a light emitting device, in particular, having a structure where a semiconductor light emitting element is sealed by a resin element.
Light emitting devices including LEDs (light emitting diodes) or other semiconductor light emitting have been widely used as various kinds of indicators, light sources, flat-type display devices, backlight of liquid crystal displays, and so forth.
The typical light emitting devices have a structure where a light emitting element is sealed by a resin in order to protect the element against a outer atmosphere or mechanical shocks.
FIG. 10 shows such a typical conventional light emitting device. The light emitting device shown here is of a so-called xe2x80x9csurface mountingxe2x80x9d type, including a package (resin stem) 800, semiconductor light emitting element 802 and sealing element 804 of a resin.
The resin stem 800 has a structure molding a pair of leads 805, 806 shaped from lead frames with a resin portion 803 of a thermoplastic resin. The resin portion 803 has an opening 801, and the semiconductor light emitting element 802 is place therein. Then the semiconductor light emitting element 802 is sealed with an epoxy resin 804.
The semiconductor light emitting element 802 is mounted on the lead 806. An electrode (not shown) of the semiconductor light emitting element 802 and the lead 805 are connected to each other by a wire 809. When en electric power is supplied to the semiconductor light emitting element 802 through those two leads 805, 806, the semiconductor light emitting element 802 emits light, and the light is extracted from an emission surface 812 via the epoxy resin 804.
The Inventor, however, made researches and has found that conventional light emitting devices of this type have still room for improvement from the viewpoint of reliability and long-time stability.
That is, through temperature cycle tests of 700 cycles under temperatures in the range from xe2x88x9240xc2x0 C. to 110xc2x0 C., various undesirable phenomena were observed, such as cracks C in the epoxy resin 804 as shown in FIG. 11, or exfoliation of the epoxy resin 804 at the interface I with the resin stem 800. In some cases, the semiconductor light emitting element 802 broke, or exfoliated from the mount surface, and the wire 809 cut down.
The light emitting device shown in FIG. 10 certainly meets the requirements currently in force, i.e., 100 cycles as the current level of temperature cycle tests requested for ordinary civilian uses, and 300 cycles for car-borne uses. However, for further improvement of the reliability toward the future uses, essential review is required.
The same circumstances commonly exist in all structures sealing semiconductor elements with epoxy resin, without being limited to that shown in FIG. 10.
As a result of a careful review of malfunctioning mechanisms, the inventor has realized that the epoxy resin 804 is physically hard and fragile and produces a large stress upon hardening and that there still exists room for improvement in the quality of close contact with the resin portion 803 of a thermoplastic resin that surrounds it.
The invention has been made upon recognition of those problems. It is therefore an object of the invention to provide a light emitting device of a type sealing a semiconductor light emitting element with a resin, which can improve the reliability and long-time stability, and can compactly mount a plurality of chips.
According to an embodiment of the invention, there is provided a light emitting device comprising: a semiconductor light emitting element; and a silicone resin provided to embed the semiconductor light emitting element, the silicone resin having a hardness not lower than 50 in JISA value.
The present application contemplates, with the term xe2x80x9csilicone resinxe2x80x9d, any resin having as its skeleton a structure in which silicon atoms having organic radicals such as alkyl radicals or aryl radicals are alternately connected to oxygen atoms. Needless to say, those containing additive elements added to such skeletons are also included in xe2x80x9csilicone resinsxe2x80x9d.